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Daily total of 500 kg of nitrogen recovered from biogas plant reject water of sewage sludge origin

Gasum’s nitrogen recycling project has shown that a daily total up to 500 kg of nitrogen can be recovered from biogas plant reject water of sewage sludge origin. The project aims to develop a recycled nitrogen product for industrial and agricultural needs.

Launched in 2015, the nitrogen recycling project is looking for viable technology for the cost-efficient recovery of nitrogen from reject water of sewage sludge origin and seeks to produce from such recovered nitrogen a recycled nitrogen product that can be used in industry, primarily for flue gas scrubbing, or as safe fertilizers in agriculture. The project is included in the programme to promote the recycling of nutrients of the Finnish Ministry of the Environment.

Gasum Biovakka (former Biovakka Suomi Oy) is the main implementer of the nitrogen recycling project, partnering in the implementation with Ekokem Corporation. The project also carries out information transfer cooperation with Finnish Water Utilities Association (FIWA) and the Baltic Sea Action Group (BSAG).

Nitrogen separation for recovery does currently not take place at all in Finnish wastewater treatment plants. In the nitrogen recycling project, nitrogen stripping equipment from the Biovakka Vehmaa biogas plant has been transferred to the Turku biogas plant, the primary feedstock of which is sewage sludge. The continuous use of the stripping equipment began in December 2015, after which various tests and optimization test runs have been conducted to adjust factors such as flow, underpressure, pH and temperature. On the basis of these tests, the functioning of the equipment has also been further developed technically, including through improved heat exchange.

The nitrogen content of ammonium water produced using the technology employed in the project is 25–28 kg per cubic meter. This means that reject water from sewage sludge can be concentrated into a recycled nutrient product with a seven times higher nitrogen concentration. Existing technologies can then be employed to concentrate the product even further. This provides a solution to the problem often faced in the production of recycled fertilizers relating to the sufficiency of recycled nitrogen. Next, the focus will be on the examination of the results of the analyses of organic contaminants and the broader viability of the technology for similar uses.

Nitrogen recovery helps the Baltic Sea

Finland’s current Government Programme sets the objective of increasing the recovery of nutrients especially in areas that are sensitive with regard to the Baltic Sea and other water bodies so that at least 50% of manure and municipal wastewater sludge will be covered by advanced processes by 2015. Cost-efficient recovery of nitrogen would contribute towards the achievement of this objective.

”The results of our nitrogen recycling project are promising, and we’re still continuing the development work. The efficient and safe utilization of recycled nutrients from feedstock streams in industry and agriculture is a significant way of reducing the burden on the environment and responding to the targets set for the circular economy,” says Planning Manager Teija Paavola from Gasum.

Gasum processes waste and produces biogas at seven biogas plants located in Turku, Vehmaa, Honkajoki, Huittinen, Kuopio, Oulu and Riihimäki. The biogas plant under construction in Riihimäki was listed as one of the Finnish Government’s key projects in February 2016. Gasum also produces biogas with its partners in Espoo, Kouvola and Lahti. In the future Gasum will produce an annual total of more than 300 GWh of 100% Finnish biogas and process a total of 425,000 tonnes of biodegradable waste a year.                  

For further information please contact:

Teija Paavola, Planning Manager, Gasum Ltd

Eeli Mykkänen, Development Manager, Gasum Ltd
Phone: +358 40 777 4327